1. Field of the Invention
The present invention relates to an optical lens system-driving control apparatus. More specifically, the present invention relates to a driving control apparatus which is incorporated in a camera having a plurality of optical lens groups movable in the optical axis direction and which control the driving of the optical lens groups, for the purpose of zooming or focusing.
2. Description of the Related Art
In a conventional photographing lens, the focusing state is adjusted by moving the lens elements, for zooming or focusing. In this type of photographing lens, the pin provided on the frame of each lens element is guided by use of a cam cylinder, and the lens elements are maintained at the positional relationships determined at the time of design.
In recent years, there has been an increased demand for a small-sized, multi-function and high-performance lens. An example of such a lens is a so-called varifocal zoom lens wherein the focal plane is moved in accordance with the movement of a power-varying lens element. The lens elements incorporated in this type of lens have to attain a large number of positional relationships predetermined beforehand, and the movement of the lens elements is complicated, accordingly.
If the lens elements require complicated movement, the cam cylinder cannot be easily designed and results in a high manufacturing cost. To solve this problem, U.S. Pat. No. 4,043,642 proposes a technique wherein the position of a power-varying lens group is detected and a correcting lens group is driven in accordance with that detection by a motor independently provided. Since small-sized motors and small-sized, high-performance calculation devices have become available in recent years, the technique disclosed in the U.S. patent enables the development of a lens arrangement which can be manufactured at less cost and permits complicated movement of lens elements with high accuracy.
The lens arrangement shown in U.S. Pat. No. 4,043,642 is comprised of a power-varying lens group having a zooming function and a correcting lens group having a focusing function. However, some of the recently-developed lenses require more complicated lens movement. A zoom lens incorporating four groups of lenses, such as the zoom lens shown in FIG. 8, is an example of such a lens. At the time of zooming, the first- to fourth-group lenses change their lens powers at different rates, and the focal plane is corrected in accordance with the change in the lens powers. At the time of focusing, the second-group and third-group lenses are moved different distances. The zoom lens shown in FIG. 8 is compact in size and has very high performance. In addition, its minimum focusing distance is very short. However, if the lens groups incorporated in the zoom lens are individually driven without employing a cam cylinder, the problems mentioned below arise.
For simplicity, the lens arrangement disclosed in U.S. Pat. No. 4,043,642 will be referred to as lens arrangement A, while the lens arrangement shown in FIG. 8 will be referred to as lens arrangement B. In the case of lens arrangement A, the factors indicating a lens state, such as a zoom value and a focal position, correspond to the position of a single lens group, and no intended focus state is produced when the lens group corresponding to the factors is driven. In the case of lens arrangement B, however, the factors indicating a lens state are associated with the positions of several lens groups. When the lens groups corresponding to the factors are driven, they may fail to have an intended positional relationship, resulting in an unexpected focus state variation, which could be caused by a lens aberration.
This problem will be described in more detail. In the case of lens arrangement A, the focal plane may be shifted in position when the group of correcting lens is driven for zooming. However, such a positional shift of the focal plane can be corrected by the technique disclosed in U.S. Pat. No. 4,043,642, and lens aberration can be maintained within a range intended at the time of design. In the case of lens arrangement B, in contrast, the first to fourth lens groups may fail to have desirable positional relationships when they are driven for zooming. If the lens groups have unintended positional relationships, various aberrations will increase, resulting in a complicated change in the focusing state.
In the case of lens arrangement B, therefore, it is required that the driving of the lens groups be controlled in such a manner that the lens groups can maintain desirable positional relationships at all times. To meet this requirement, it has been proposed to adopt the technique wherein a change in the factors (zooming and focusing) is controlled by causing a calculation device to calculate the driving parameters (such as a target position) of each lens group. However, this technique is not practical, since the load applied to the calculation device increases too much and since desirable position relationships among the lens groups are not always maintained.
Conventionally, focusing has been performed in two techniques with respect to the photographing lens of a camera. One is a method wherein all lens groups are advanced, while the other is a method wherein part of the lens groups are advanced. Of these two techniques the second technique recently draws the attention of those skilled in the art since the lens driving distances are short, as is seen in inner focusing.
A high-level technique has been derived from the second technique. An example of such a technique is a so-called floating technique wherein two or more lens groups are moved in different ways at the time of focusing, so as to suppress the aberration.
Under these circumstances, a photographing lens having a zooming or focusing function has been employed in a camera. In the photographing lens, the pin provided on the frame of each lens group is guided by the cam groove formed in a cam cylinder such that all lens elements are moved in predetermined ways.
Where the cam cylinder is employed, it is difficult to use the floating technique since the movement of each lens group is dependent on the cam cylinder. Further, in many zoom lenses (the demand for the zoom lenses is great these days), the optimal floating states needed to suppress the aberration related with focusing differ in accordance with different zoom states, such as a wide-angle state and a telephoto state.
Where a zoom lens employs a focusing mechanism of a floating type, a single floating state is determined such that the lens groups are moved in a suitable manner from a wide angle, (when short-distance photographing) to a photographing and are moved in a suitable manner for the telephoto focus position, when long-distance photographing occurs such that the single floating state suppress the overall aberration to the possible degree. With this technique, however, the aberration cannot be suppressed, depending upon the zoom state or the distance to an object to be photographed. It is therefore difficult to design a high-performance zoom lens.
According to U.S. Pat. No. 4,161,756, the positional relationships among a plurality of lens groups are stored in a memory (such as a ROM) as digital-value data. On the basis of the digital-value data and the positional information obtained by actual measurement, the lens groups are driven independently of one another, with no need to use a cam groove.
If the driving of the lens groups is controlled on the basis of in accordance with the technique disclosed in U.S. Pat. No. 4,161,756, it may be thought that the load applied to the calculation device can be decreased and that the aberration can be suppressed using the single floating state. However, if the positional information regarding the driving control of all lens groups is stored in the memory, the amount of data required will be very large. Since the storage capacity of the memory is limited, it is not practical to store all positional information.